1. Related Art
Rapid Prototypying and Manufacturing (RP&M) is the name given to a field of technologies that can be used to form three-dimensional objects rapidly and automatically from three-dimensional computer data representing the objects. RP&M can be considered to include three classes of technologies: (1) Stereolithography, (2) Selective Deposition Modeling, and (3) Laminated Object Manufacturing.
The stereolithography class of technologies create three-dimensional objects based on the successive formation of layers of a fluid-like medium adjacent to previously formed layers of medium and the selective solidification of those layers according to cross-sectional data representing successive slices of the threedimensional object in order to form and adhere laminae. One specific stereolithography technology is known simply as stereolithography and uses a liquid medium which is selectively solidified by exposing it to prescribed stimulation. The liquid medium is typically a photopolymer and the prescribed stimulation is typically visible or ultraviolet electromagnetic radiation. Liquid-based stereolithography is disclosed in various patents, applications, and publications of which a number are briefly described in the Related Applications section hereinafter. Another stereolithography technology is known as Selective Laser Sintering (SLS). SLS is based on the selective solidification of layers of a powdered medium by exposing the layers to infrared electromagnetic radiation to sinter or fuse the particles. SLS is described in U.S. Pat. No. 4,863,538 to Deckard. A third technology is known as Three Dimensional Printing (3DP). 3DP is based on the selective solidification of layers of a powdered medium which are solidified by the selective deposition of a binder thereon. 3DP is described in U.S. Pat. No. 5,204,055 to Sachs.
The present invention is primarily directed to stereolithography using liquid-based building materials (i.e. medium). The present invention presents techniques for building high resolution objects by overcoming recoating problems that can exist when using such a medium. It is believed, however, that the techniques of the present invention may have application in the other stereolithography technologies for the purposes of enhancing resolution and/or reducing distortion.
Selective Deposition Modeling, SDM, involves the build-up of three-dimensional objects by selectively depositing solidifiable material on a lamina-by-lamina basis according to cross-sectional data representing slices of the three-dimensional object.
One such technique is called Fused Deposition Modeling, FDM, and involves the extrusion of streams of heated, flowable material which solidify as they are dispensed onto the previously formed laminae of the object. FDM is described in U.S. Pat. No. 5,121,329 to Crump. Another technique is called Ballistic Particle Manufacturing, BPM, which uses a 5-axis, ink-jet dispenser to direct particles of a material onto previously solidified layers of the object. BPM is described in PCT publication numbers WO 96-12607; WO 96-12608; WO 96-12609; and WO 96-12610, all assigned to BPM Technology, Inc. A third technique is called Multijet Modeling, MJM, and involves the selective deposition of droplets of material from multiple ink jet orifices to speed the building process. MJM is described in U.S. patent application Ser. Nos. 081722,326, filed Sep. 27, 1996, and 08/722,335, filed Sep. 27, 1996, (both assigned to 3D Systems, Inc. as is the instant application). Laminated Object Manufacturing, LOM, techniques involve the formation of threedimensional objects by the stacking, adhering, and selective cutting of sheets of material, in a selected order, according to the cross-sectional data representing the three-dimensional object to be formed. LOM is described in U.S. Pat. No. 4,752,352 to Feygin; and U.S. Pat. No. 5,015,312 to Kinzie, and in PCT Publication No. WO 95-18009 to Morita.
Though, as noted above, the techniques of the instant invention are directed primarily to liquid-based stereolithography object formation, it is believed that the techniques may have application in the SDM technologies to enhance object resolution for a given droplet or stream size and/or to reduce object distortion. It is further believed that the techniques may have application in the LOM technologies to enhance object resolution when a minimum cutting depth is greater than the thickness of the individual sheets being used to form the object.
Various techniques for enhancing the resolution of three-dimensional objects formed using stereolithography have been described previously. In particular various techniques have been described in (1) U.S. Pat. No. 5,597,520 and its CIP, U.S. patent application Ser. No. 08/428,951, filed Apr. 25, 1995, both to Smalley, et. al; (2) EP Laid Open Patent Application Publication No. 388 129 to Yamamoto; (3) U.S. Pat. No. 5,209,878 to Smalley, et.al; (4) Japanese Laid Open Patent Application Publication No. 2-95830A to Nakamura et.al; and (5) Japanese Laid Open Patent Application Publication No. 2-95831A to Kuribayashi, et. al.
The '520 patent and '951 application describe the use of Simultaneous Multiple Layer Curing Techniques in Stereolithography. These techniques address issues related to the formation of objects with resolution which is finer than a Minimum Solidification Depth (hereafter "MSD") possessed by the building material. These techniques further address the formation of objects with finer resolution than a Minimum Recoating Depth (hereafter "MRD") associated with the building material. MRD may be defined as the minimum thickness of coatings that can be reliably formed over previously solidified laminae. In strict layer-by-layer object formation, the MRD sets the minimum layer thickness that can be reliably used in forming the object. To obtain a desired resolution which is finer than the MRD (i.e. layer thickness thinner than the MRD), the techniques described in this application require complex data manipulations. There is a desire in the art for simpler techniques that can enhance resolution, while relying on less complex algorithms and building techniques (e.g. ones that use simpler data handling techniques).
Yamamoto, the '129 publication, discloses the use of boundary exposures in association with alternating layers (i.e. layers N, N+2, N+4, etc.) and the use of raster exposures to solidify internal portions of laminae in association with the opposite alternating layers (i.e., N+1, N+3, N+5, etc.). According to the teachings of this reference, each pair of consecutive layers is exposed with the same shape, one exposing boundaries and the other exposing internal regions. The resolution increment for an object produced according to the teachings of this reference is equal to two layer thicknesses. The exposure of boundaries solidifies the material associated with the layer of the boundary only; while the exposure of internal regions solidifies material associated with not only the layer of exposure, but the previous layer as well. This publication does not achieve enhanced object resolution. Achieved object resolution is not based on the thickness of a single layer (i.e. thickness between consecutively applied coatings). This publication does not address the need for enhanced resolution, let alone the need for enhanced resolution in view of an MRD which is larger than desired. Furthermore, this reference fails to address any techniques for handling formation of outward facing regions that may be associated with any given lamina.
Smalley, et al., in the '878 patent, discloses the use of thick structural laminae in combination with thin fill laminae and/or meniscus smoothing to fill discontinuities at the edges of the thick structural laminae. These thin fill laminae or meniscus regions form a portion of the outward-facing, sloped regions of an object. This reference does not address recoating difficulties (e.g. MRD related issues) that may limit the ability to form the thin layers desired.
Nakamura, et al., in the '830 publication teaches a technique for reducing discontinuities between thick layers which form the interior portion of the object by forming thin fill layers in exterior regions of the object. As with the '878 patent, this publication does not address recoating difficulties (e.g. MRD related issues) that may limit the ability to form the thin layers desired.
Kuribayashi, et al., in the '831 publication teaches a technique for reducing discontinuities between thick layers by filling in these discontinuities with resin and then exposing the resin within the discontinuities to solidifying radiation. This technique leads to improved surface finish, but fails to provide a building technique that achieves enhanced object resolution when recoating difficulties exist.
All patents, applications, and publications referred to in this section are hereby incorporated by reference as if set forth in full.
A need exists in the art for simplified techniques that can be used to form objects having a desired resolution finer than that reliably allowed by the MRD of the material (i.e. the MRD associated with forming coatings over entire cross-sectional laminae).
2. Other Related Patents and Applications
The patents and applications in the following table are hereby incorporated by reference herein as if set forth in full. The gist of each patent and application is included in the table to aid the reader in finding specific types of teachings. It is not intended that the incorporation of subject matter be limited to those topics specifically indicated, but instead the incorporation is to include all subject matter found in these applications and patents. The teachings in these incorporated references can be combined with the teachings of the instant application in many ways. For example, the references directed to various data manipulation techniques may be combined with the teachings herein to derive even more useful, modified object data that can be used to more accurately and/or efficiently form objects. As another example, the various apparatus configurations disclosed in these references may be used in conjunction with the novel features of the instant invention.
TABLE 1 __________________________________________________________________________ Related Patent and Applications Patent No. Application No. Inventor Subject __________________________________________________________________________ 4,575,330 Hull Discloses fundamental elements of stereolithography. 4,999,143 Hull, et al. Discloses various removable support structures applicable to stereolithography. 5,058,988 Spence Discloses the application of beam profiling techniques useful in stereolithography for determining cure depth and scanning velocity, etc. 5,059,021 Spence, et al. Discloses the utilization of drift correction techniques for eliminating errors in beam positioning resulting from instabilities in the beam scanning system 5,076,974 Modrek, et al. Discloses techniques for post processing objects formed by stereolithography. In particular exposure techniques are described that complete the solidification of the building material. Other post processing steps are also disclosed such as steps of filling in or sanding off surface discontinuities. 5,104,592 Hull Discloses various techniques for reducing distortion, and particularly curl type distortion, in objects being formed by stereolithography. 5,123,734 Spence, et al. Discloses techniques for calibrating a scanning system. In particular techniques for mapping from rotational mirror coordinates to planar target surface coordinates are disclosed 5,133,987 Spence, et al. Discloses the use of a stationary mirror located on an optical path between the scanning mirrors and the target surface to fold the optical path in a stereolithography system. 5,174,931 Almquist, et al. Discloses various doctor blade configurations for use in forming coatings of medium adjacent to previously solidified laminae. 5,182,056 Spence, et al. Discloses the use of multiple wavelengths in the exposure of a stereolithographic medium. 5,182,715 Vorgitch, et al. Discloses various elements of a large stereolithographic system. 5,184,307 Hull, et al. Discloses a program called Slice and various techniques for from app. no. converting three-dimensional object data into data descriptive 07/331,644, filed of cross-sections. Disclosed techniques include line width March 31, 1989 compensation techniques (erosion routines), and object sizing techniques. The application giving rise to this patent included a number of appendices that provide further details regarding stereolithography methods and systems. 5,209,878 Smalley, et al. Discloses various techniques for reducing surface discontinuities between successive cross-sections resulting from a layer-by-layer building technique. Disclosed techniques include use of fill layers and meniscus smoothing. 5,234,636 Hull, et al. Discloses techniques for reducing surface discontinuities by coating a formed object with a material, heating the material to cause it to become flowable, and allowing surface tension to smooth the coating over the object surface. 5,238,639 Vinson, et al. Discloses a technique for minimizing curl distortion by balancing upward curl to downward curl. 5,256,340 and Allison, et al. Discloses various build/exposure styles for forming objects 08/766,956, filed including various techniques for reducing object distortion. December 16, 1996 Disclosed techniques include: (1) building hollow, partially hollow, and solid objects, (2) achieving more uniform cure depth, (3) exposing layers as a series of separated tiles or bullets, (4) using alternate sequencing exposure patterns from layer to layer, (5) using staggered or offset vectors from layer to layer, and (6) using one or more overlapping exposure patterns per layer. 5,321,622 Snead, et al. Discloses a computer program known as CSlice which is used to convert three-dimensional object data into cross-sectional data. Disclosed techniques include the use of various Boolean operations in stereolithography. 5,597,520 and Smalley, et al. Discloses various exposure techniques for enhancing object 08/428,951, filed formation accuracy. Disclosed techniques address formation April 25, 1995 of high resolution objects from building materials that have a Minimum Solidification Depth greater than one layer thickness and/or a Minimum Recoating Depth greater than the desired object resolution. 08/722,335, filed Thayer, et al. Discloses build and support styles for use in a Multi-Jet September 27, 1996 Modeling selective deposition modeling system. 08/722,326, filed Earl, et al. Discloses data manipulation and system control techniques for September 27, 1996 use in a Multi-Jet Modeling selective deposition modeling system. 08/790,005, filed Almquist, et al. Discloses various recoating techniques for use in January 28, 1997 stereolithography. Disclosed techniques include 1) an ink jet dispensing device, 2) a fling recoater, 3) a vacuum applicator, 4) a stream recoater, 5) a counter rotating roller recoater, and 6) a technique for deriving sweep extents. 08/847,855, filed Partanen, et al. Discloses the application of solid-state lasers to April 28, 1997 stereolithography. 08/792,347, filed Partanen, et al. Discloses the use of a pulsed radiation source for solidifying January 31, 1997 layers of building material and in particular the ability to limit pulse firing locations to only selected target locations on a surface of the medium. 08/855,125, filed Nguyen, et al. Discloses techniques for interpolating originally supplied cross- May 13, 1997 sectional data descriptive of a three-dimensional object to produce modified data descriptive of the three-dimensional object including data descriptive of intermediate regions between the originally supplied cross-sections of data. 08/854,950, filed Manners, et al. Discloses techniques for identifying features of partially formed May 13, 1997 objects. Identifiable features include trapped volumes, effective trapped volumes, and solid features of a specified size. The identified regions can be used in automatically specifying recoating parameters and or exposure parameters. __________________________________________________________________________
The following two books are also incorporated by reference herein as if set forth in full: (1) Rapid Prototyping and Manufacturing: Fundamentals of Stereolithography, by Paul F. Jacobs; published by the Society of Manufacturing Engineers, Dearborn Mich.; 1992; and (2) Stereolithography and other RP&M Technologies: from Rapid Prototyping to Rapid Tooling; by Paul F. Jacobs; published by the Society of Manufacturing Engineers, Dearborn Mich.; 1996.